Electrolysis of alpha, beta mono-olefinic carboxylates



3,193,432 Patented July 6, 1965 United States Patent Office 3,193,482 ELECTRGLYSi-S F can MQNU-GLEFHNZC CARBUXYLATES Manuel M. Rainer, St. Louis, M0,, assignor to Monsanto Company, a corporation of Delaware No Drawing. Filed .lan. 14, 1964, Ser. No. 337,540 25 (Claims. (Ci. Mi t-73) This application is a continuation-in-part of my copending application Serial No. 75,130 filed December 12, 1960, and now forfeited; my copending application Serial No. 145,482 filed October 16, 1961, and now abandoned; my copending application Serial No. 189,- 072 filed April 20, 1962; and my copendingapplication Serial No. 234,833 filed November 1, 1962, and now abandoned.

This invention relates to the manufacture of polyfunct-ional compounds and more particularly provides a new and valuable electrolytic process for the hydrodimerization of alpha,beta-mono-olefinic carboxylates.

The present invention is concerned with the hydrodimerization, i.e., the reductive dimerization, of certain olefinic compounds to obtain saturated dimers thereof.

A general object of the invention is the provision of an improved process for the preparation of alkane dior tetra-carboxylates. A further object is the provision of a technically feasible, electrolytic process for the conversion of alpha,beta-mono-olefinic monoor di-carboxylates to paraflinic dior tetra-carboxylates. Yet another object is the electrolytic conversion of aliphatic alpha, beta-olefinic mono-carboxylates to paraifinic dicarboxylates. A further object is the electrolytic onversion of aliphatic alpha-beta-olefinic dicarboxylates to paraflinic tetra-carboxylates. An important object of the invention is the provision of an electrolytic process of converting aliphatic alpha,beta-mono-olefinic carboxylates to obtain good yields of the saturated dimers thereof rather than a preponderance of hydrogenated monomers and/or complex organometallic compounds.

These and other objects of the invention hereinafter described are provided by the present process for conducting the hydrodimerization of an aliphatic alpha,betamono-olefinic carboxylate of, for example, from 3 to 8 carbon atoms, which comprises subjecting to electrolysis, in contact with a cathode, a solution of the olefinic compound in an aqueous electrolyte under non-polymerizing conditions such that the desired hydrodimer is obtained and recovered in good yield. It is desirable to employ fairly concentrated solutions in order to minimize undesired reactions of intermediate ions with the water of the electrolyte; The average amount of the carboxylate reactants will be at least about 5% by weight of the catholyte, and preferably at least 10% by weight or more. The process is characterized by fairly high concentrations of salts in the catholyte, consisting at least 5% by weight of the catholyte and usually constituting or more by weight of the total amount of salt and water in the catholyte, in order to obtain the desired solubility of the olefinic compounds and the desired conductivity.

The salt concentration has an important bearing upon the results obtained. When the salts are hydrotrop-lc, high concentrations contribute to solubility of the alpha, beta-olefinic carboxylates, making it possible to utilize higher concentrations of the carboxylates. But beyond this, the concentration of salt cations in some way aifects the course of the reaction and results in higher yields of hydrodimers at the expense of simple reduction products. The'process of the present invention is carried out utilizing a supporting electrolyte as understood by those in the art, i.e., electrolyte capable of carrying current but not discharging under the electrolysis conditions, but with the erization will not occur.

requirement that the supporting electroyltebe a salt and that it constitute at least 5% by weight of the solution electrolyzed. The requirements of supporting electrolytes are well understood by those skilled in the art and they will be able to select such electrolytes and utilize them in the proper concentrations in view of the teaching herein as to catholyte required for hydr0- dimerizations of alpha,beta-olefinic carboxylates, and salt concentrations essential to such hydrodimerizations. As the hydrodimerization of ethyl acrylate, for example, proceeds at the cathode voltages which can vary circa -l.85 (vs. saturated calomel electrode), depending somewhat upon conditions, any electrolyte salts not subject to substantial discharge at less negative conditions can be employed, and to some extent those discharging at about ,1.75 to 1.85 volts (vs. saturated calomel electrode). Thus, extensive classes of suitable electrolyte salts areavailable for use. The salts can be organic or inorganic, or mixtures of such, and composed of simple cations and anions or very large complex cations and anions. The term salts is employed herein in its generally recognized sense to indicate a compound composed of a cation and an anion, such as produced by reaction of an acid with a base.

It is preferred that the salts employed herein have the properties of that class of salts recognized as hydrotropic, i.e., as promoting the solubility of organic compounds in water. Various organic sulfonates, alkyl sulfates, etc., have hydrotropic effects. In this application any salt which increases the solubility of olefinic carboxylates in water is considered hydrotropic.

.Some olefinic compounds are subject to polymerization or other side reactions if the electrolyte is acidic, or excessively alkaline, and it will be desirable in such cases to conduct the reductive coupling in solutions which are not overly acidic and also in some cases below a pH at which undesirable side reactions occur, e.g., below about 12. To minimize polymerization, simple reduction of the olefinic bond and other side reactions, the pH is usually maintained in the range of about 3 to about 12, preferably 6 to 9.5. In addition, which the catholyte during electrolysis is acidic, it will generally be advisable to conduct the electrolysis under conditions which inhibit polymerization of the reactants involved or in the presence of a polymerization inhibitor, for example, in an atmosphere containing sutficient oxygen to inhibit the polymerization in question, or in the presence of inhibi tors effective for inhibiting free radical polymerization. Classes of inhibitors for inhibiting free radical polymerizations are well known, e.g., such inhibitors as hydroquinone, p-t-butyl catechol, quinone, p-nitrosodimethylaniline, di-t-butyl hydroquinone, Z-S-dihydroxy-1,4-benzoquinone, 1,4-naphthoquinone, chloranil, 9,10-phenanthraquinone, 4-amino-l-naphthol, etc., are suitable. The present process will ordinarily be conducted in the absence of free radical polymerization catalysts or materials which will form polymerization catalysts under the electrolysis conditions, although their presence is not' necessarily undesirable if polymerization is sufliciently inhibited or conditions are otherwise such that polym- The inhibitors are ordinarily used in small amounts, e.g., less than 1% by weight based on the olefinic carboxylate, for example 0.01% by weight based on the olefinic carboxylate, but can be used in larger amounts such as up to 5% or more by weight, based on the olefinic carboxylate.

Even though suitable inhibitors are employed, the

yields are generally markedly better under conditions which are not greatly acidic. However, the deleterious efiects of acidity can be to some extent overcome by use of fairly high current densities, such as over '10 amperes/ dm. of cathode surface, and a rapidly circulating electrolyte system; this may be due to the supply of electrons on the cathode surface making such surface alkaline despite acidity in the bulk of the solution. In addition high salt concentrations mitigate the effect of acidity by carrying a large share of the current, particularly at high current densities. Even under acidic conditions, the concentration of the salt cation which does not discharge under the electrolysis conditions is markedly greater than that of the hydrogen ion. For example even at a pH of 2, the hydrogen ion concentration is only 0.01 N, which is many times less than the usual salt cation concentration. In

' fact, the concentration (normality) of the salt cation will generally be at least times that of the hydrogen ion and often 100 times that of the hydrogen ion. The effect of small amounts of cations which discharge at less nega tive potentials can similarly be masked by high eerie-em trations of. more suitable cations. For example, in the case of ethyl acrylate sodium orfpotassium salts can definitely be used as supporting electrolyte, but their use results in lower yields as will be discussed in more detail hereinbelow, and for this reason it is definitely preferred to utilize salt cations of more negative discharge poten tials than sodium. However, small amounts of sodium ally of from 1 to 5 carbon atoms.

Methyl ac'rylate is thus converted to dimethyl adipate:

0 o H COi. l-CHzCH2CHzCH9 -OCH3 The alpha,beta-olefinic dicarboxylates are hydtodime rized by the presently provided process to give parafiinic tetracarboxylates:

or potassiumsalts, such as 2 or 3% by weight of the tion, and much greater amounts can, of course be em= ployed. However, lower concentrations can be' used, particularly if polar solvents are used along with the water and salt, although it is preferred on'a cost basis to avoid the use of polar solvents. It will be recognized that the 7 pH considerations with respect to the catholyte solution make it desirable to avoid any concentration of highly basic or acidic salts.

In addition to the foregoing considerations, a number 7 of other factors are important in selecting salts suitable for good results. For example, it is undesirable that the salt cation form an insoluble hydroxide at the operating pH, or that it discharge on the cathode forming an alloy which substantially changes the hydrogen over-voltage and leads to poorer current efficiencies. The salt anion should not be lost by discharge at the anode with possible formation of by-products. If a cell containing a separating membrane is used, 'it is desirable to avoid types of anions which, in contact with hydrogen ions present in the anolyte chamber, would form insoluble acids and clog the pores of the membrane.

In general amine and quaternary ammonium salts'are suitable for use in the present process. Alkali and alkaline earth metal salts can also be used, although the'alkali metals are somewhat more subject to interfering discharge, and the'alkaline earth metal salts tend to have poor water solubility. V

' According to the presently provided process, the alpha,

beta-olefinic mono-carboxylates are converted by the p'resa cut process to paraffinic dicarboxylates:

wherein Y'is an alkyl of aryl radical, preferably of from where R, R and Y are as above defined.

Propyl maleate is thus converted to tetrapropylbutane- 1,2,3,4-tetracarboxylate. I

The 1,2-olefinic dicarboxylates in which the two carboxylate groups are on the same carbon atom, i.e., methylene malonates, are similarly hydrodimerized:

Where R and Y are as above defined. Diethyl ethylidene-malonate is thus converted to tetraethyl 2,3-dimethylbutane- 1, l ,4,4-tetracarboxylate.

While the molecular size of the olefinic compounds to be reductively dimerized is not controlling, in general olefinic compounds containing more than 20 carbon atoms will be of little or no interest; It is generally preferable that the carboxylate group be the only functional group other than the olefinic double bond, i.e., that the compound be saturated hydrocarbon except for the olefinic bond and the carboxylate groups, viz. l-carbalkoxy-alkyl-l-enes.

Hydrodimerization by the present process of various alkyl or aryl esters of aliphatic alpha,beta-olefinic monoor dicarboxylates is shown in the table below, wherein the v alpha,beta-olefinic monomeric compound and the satu rated dimer obtained therefrom are given. The hydrodrmerization product is that to be expected from headto-head addition, i.e., coupling at the carbon atom beta-I to the functional group, e.g., ethyl cro-tonate is converted by the present process to diethyl 3,4-dimethyladipate.

Ethyl erotouate Diethyl 3,4-dimethyl-adipate.

Methyl-2-1sopr0pylcrotonate Dlmethyl 2,5-diis0propyl-3,4-

dimethyladipate.

Butyl tiglate Dibutyl 2,3,4,fi-tetramethyladipate,

Pentyl aerylate Dipentyl adipate. 1

Ethyl Z-pentenoate- Diethyl 3,4-diethyladipate.

Isopropyl senecloate- Diisopropyl 3,3,4,4-tetramethyladi at Pentylfumarate Tetrapent butane-1,2,3,4-tetracarboxylate.

Ethyl cltraconatc Tetraethyl hexane-2,3, 1,5-tettacarboxylate The aromatic or aromatic-aliphatic esters of the alpha, beta-mono-olefinic carboxylic acids, e.g., phenyl acrylate or di-p-tolyl maleate or benzyl propyl fumarate are similarly hydrodimerized according to the present process.

When working with some of the substituted acrylic or maleic acids there is often obtained a mixture of steroisomeric hydrogenated dimers. For most industrial uses, however, e.g., for preparation of condensation polymers, both isomers are useful; so that generally no occasion arises for requiring separation of the two isomers. However, if desired, this may be effected by methods known to those skilled in the art, e.g., close fractional distilla tion, crystallization, etc.

In carrying out the process of this invention, a solution for electrolysis is prepared by adding the alpha,betamono-olefinic carboxylate to a strong aqueous solution (about 30% or more by weight) of the conducting salt to give a solution which contains at least 5% by weight, based on the total weight of the solution, of the olefinic carboxylate in the dissolved state. Depending upon the quantity of salt present and the nature thereof, there may thus be obtained true solutions containing as much as 50% or more by weight of the olefinic carboxylate. The concentration of olefinic carboxylate in the dissolved state is to some extent a function of salt concentration; however, at temperatures of above room temperature, i.e., at above, say, 35 C., less of the salt is required to obtain optimum concentration of dissolved olefinic carboxylate than is required at room temperature. Because the extent of hydrodimerization appears to be related to the concentration of the olefinic carboxylate in the electrolysis solution, when the electrolysis is to be conducted at room temperature, the olefinic carboxylate is advantageously added to a saturated aqueous solution of the salt in order to obtain thereby as high a concentration as possible of the dissolved olefinic carboxylate. When the electrolysis is to be conducted at a temperature of above room temperature, high concentrations of olefinic carboxylate can be attained with unsaturated solutions of the salt, i.e., the salt may be as low as 30% by weight of the electrolysis solution. Concentration of the olefinic carboxylate in the electrolysis solution may also be increased by using a mixture of water and a polar solvent, e.g., acetonitrile, dioxane, ethylene glycol, dimethylformamide, dimethylacetamide, ethanol or isopropanol, together with the aromatic salt.

An electrolytic cell preferably having a cathode of high hydrogen overvoltage is charged with the thus prepared solution and an electric current is passed through the cell to effect the hydrodimerization reaction. Depending upon the concentration of the olefinic carboxylate and upon the hydrogen ion concentration of the solution, there may or may not be formed products other than the saturated dimer. Thus, when working with concentrations of olefinic carboxylate which are less than or from 10 to by weight of the solution, there may be formed, in addition to the hydrodimerization product, compounds such as the reduced monomers or other condensation products. With ethyl acrylate, for example, ethyl propionate may thus be obtained as by-product. The hydrogen ion concentration of the solution will ordinarily be such as to give a pH of 7 or higher, as neutral or mildly alkaline solutions are ordinarily preferred. Many of the alpha,beta-mono-olefinic carboxylates tend to polymerize when electrolyzed in strongly acidic solutions, such as solutions of mineral acids, and it is desirable or almost necessary in such cases to avoid excessive acidity, making it desirable to operate at pHs above about 5 or 6, such as provided by solutions of salts of strong bases. Moreover, the hydrogen ion has a cathode discharge potential of about 1.5 volts, making it desirable toavoid high concentrations of hydrogen ion in the catholyte if the reduc tive coupling occurs at similar or more negative cathode potentials. The reductive couplings can suitably be con 6 ducted at pHs higher than those at which substantial polymerization of olefinic compound occurs, or higher than pHs at which there is undue generation of hydrogen, for example, at pHs higher than those at which more than half the current is expended in discharging hydrogen ions. The pHs referred to are those obtaining in the bulk of the catholyte solution, such as determinable by a pH meter on a sample of the catholyte removed from the cell. The electrolysis in effect generates acid at the anode and base at the cathode; it will be recognized that in an undivided cell the pH in the immediate vicinity of the cathode may differ considerably from that near the anode, particularly if good stirring is not employed. To some extent the effects of acidity can be counteracted by high current density to cause more rapid generation of hydroxyl ions. However, high current densities also require good stirring or turbulence to move the reactants to the cathode.

During electrolysis in a divided cell, alkalinity increases in the catholyte. However, the anolyte becomes acidic. When a porous diaphragm is used to separate the catholyte from the anolyte, the alkalinity of the catholyte will depend upon the rate of diffusion of acid from the anolyte through the porous barrier. Control of alkalinity in the catholyte, when employing a diaphragm, may thus be realized by purposely leaking acid from the anolyte into the catholyte. it can also be achieved, of course, by extraneous addition to the catholyte of an acid material, e.g., glacial acetic acid, phosphoric acid or p-toluenesulfonic acid. Alkalinity may also be controlled, whether or not a diaphragm is used in the cell, by employing buffer systems of cations which will maintain the pH range while not reacting at the reaction conditions. Control of alkalinity becomes particularly necessary if the electrolytic hydrodimerization is carried to a high conversion, or if it is conducted in a continuous manner with continuous or intermittent addition of carboxylate and removal of product, while the electrolyte itself stays in the cell or is recycled to the cell. While a successful hydrodimerization could be successfully conducted for some period of time without provisions to counteract the alkalinity, it is apparent that eventually the build-up of hydroxyl ions in the catholyte of a divided cell would be such as to cause undesirable side-reactions to predominate. Therefore, for high conversion or continuous procedures it is necessary to employ a means for controlling the alkalinity. In general it is undesirable that the alkalinity rise so high as to tend to cause substantial hydrolysis of the carboxylate reactant and it will be desirable to maintain the pH at values no greater than 9.5 or 10, although higher pHs can be employed. Good agitation or turbulence counteracts excess alkalinity to some extent, by minimizing local concentrations of hydroxyl ions at the cathode, making it possible to operate efficiently at higher bulk pHs. Moreover, good agitation maintains a suitable carboxylate concentration near the cathode and keeps the electrolysis rate and use of high current densities from being unnecessarily limited by slow diffusion rates. Agitation as used herein is intended to include movement of the electrolysis medium whether resulting from stirring, beating, vibration, pumping or bubbling fluids through the medium, circulation of the medium itself, with or without bathing, and various other means of causing currents in the electrolyte medium or admixture of the components thereof.

Theterm consisting essentially of as employed herein with respect to the solutions electrolyzed is intended to leave the'solutions open to addition of other components which do not change the basic nature of the solutions with respect to the electrolytic hydrodirnerization process being conducted therein.

When a divided cell is employed, it will often be desirable to use an acid as the anolyte, any acid being suitable, particularly dilute mineral acids such as sulfuric or phosphoric acid. Hydrochloric acid can be employed but would have the disadvantage of generating chlorine at the anode, and of being more corrosive with respect to some anode materials. If desired, a salt solution can be used as anolyte, those useful as catholyt-e also being suitable as :anolyte, although there are many other salt solutions suitable for such use. It will be recognized that the descriptions of the catholyte or oarboxylate solutions herein apply to the solutions, regardless of whether they are in an undivided cell serving'as hoth catholyte and an-olyte, or are in the cathode-containing portion of a divided cel'l. Conversely, when a divided cell is employed, the various descriptions of the cath-olyte' do not necessarily apply to the .anolyte, as the olefinic carhoxylate is not ordinarily present in the anolyte and the character of the anolyte is not of primary importance to the hydrodimerization reaction which is occurring in the cath-olyte. A a practical matter, to obtain good yields in the operation of a continuous process over a matter of days or weeks, it may be necessary to employ a divided cell to avoid or. minimize interfering reactions, such as resulting from generation of hydrogen ions at the anode or resulting in deposition of various salt materials on the .anode. Moreover, many suitable catholy-te salts are subject to degradation if permitted to contact the anode, making it advantageous to employ mineral acids as the .anolyte in a divided cell.

In the past various electrolysis reactions for reducing or otherwise altering organic compounds have been known. In general, however, such reactions have had the disadvantage of being of small scale and low velocity and requiring careful control of many conditions. Quite often such reactions could not be scaled-up by using high current densities to give practical production rates and therefore remained laboratory curiosities. In contrast, the present process operates very effectively at current densities of greater than 1 amperes/square *decimeter of cathode surface, and the most suitable densities may be in the range of 15 to 20 to 40 or 50 amperes/square decimeter and higher, even up to 100 or more amperes/square decimeter, and it is further possible to use cells having a large effective electrode area, whether in a single set of electrodes or in a series of electrodes. Thus in commercial practice it is probable that individual cells will draw at least 20 to 30 amperes, most likely more than 100 amperes, and cells drawing more than 1000 amperes are contemplated. For reasons of economics and to make practical use of such current densities without necessitating prohibitively high cell voltages, it is essential to have fairly low resistance in the cell as obtainable by utilizing fairly high concentrations of the electrolyte salt and a relatively narrow gap between the electrodes, e.g., no more than one-half inch, and preferably of the order of one-fourth inch or smaller. Applied voltages of 5 to 20 volts for current densities of to 40 amperes/d-m. are suitable, and it is preferable, in this range as well as at higher densities that the applied voltage have a numerical value no greater than one-half the numerical value of the current density (in amperes/dm. Various power sources are suitable for use in the present invention, particularly any efiicient sources of direct current, and, if desired, various known means of varying the applied po tential to regulate the current density and the cathode potential can .be employed, for example thermeans described in Metcalf et al., US. Patent No. 2,835,631 issued May ,20, 1958, the disclosure of which is incorporated herein by reference. If desired alternating current can be superimposed on the direct current applied to the cell. Materials suitable for constructing the electrolysis cell employed in the present process are well known to those skilled in the art. The electrodes can be of any suitable cathode and anode material. The anode may be of virtually any conductor, although it.will usually bezad vantageous to employ those that are. relatively inertor attacked or corroded only slowly by the electrolytes; suitable anodes are, for eirample, platinum,"'carbon, gold, nickel, nickel silicide, Duriron, lead, and lead antimony 8 .and lead-copper alloys, and alloys of various of the fore going and other metals.

Any suitable material can be employed as cathode, various jmetals and alloys being known to the art. It is generally advantageous to employ metals of fairly high hydrogen over-voltage in order to promote current efiiciency and minimize generation of hydrogen during the electrolysis. In general it will be desirable to employ cathodes having overvoltages at least about as great a that of copper, as determined in a 2 N sulfuric acid solution at current density of 1 rnilliamp/square centimeter (Oarman, Chemical Constitution and Properties of'Engineering Materials, Edward Arnold and (10., London, 1949', page 290)., Suitableelectrode materials include, for example, mercury, cadmium, tin, zinc, bismuth, lead, graphite, aluminum, nickel, etc., in general those of higher overvoltage being preferred, although those of lower hydr-ogen'overvoltage can also be employed, even if they cause generation of hydrogen under the electrolysis conditions, as is the case with stainless steel and other electrodes of lower hydrogen overvoltage. It will 'be realized that overvoltage can vary with the type of surface and prior history of the metal as well as with other factors; therefore the'term overvoltage as used herein with respect to copper as a gauge has reference to the overvoltage under the conditions of use in electrolysis.

Among the salts which can be employed according to the invention for obtaining the desired concentration of dissolved olefinic carboxylate, the amine and quaternary ammonium salts are generally suitable, especially those of sulfonic and alkyl sulfuric acids. Such salts can be the saturated aliphatic amine salts or heterocyclic amine salts, e.g., the.mono-,' dior trialkylamine salts, 'or the mono-', 'di-. or trialkanolamine salts, or the piperidine, pyrrolidine or morpholine salts, e.g., the ethylamine, dimethylamine or triisopropylamine salts of various acids especially various sulfonic acids. Especially preferred are aliphatic and 'heterocyclic quaternary ammonium salts, i.e., the tetraalkylammonium or'the tetraalkanolammonium salts or mixed alkyl alkanol ammonium salts such as the'alkyltrialkanolammoniurn, the dialkyldialkanolammonium, the alkanoltrialkylammonium or the N-heterocyclic'N-alkylammonium salts of sulfonic or other suitable acids. The saturated aliphatic or heterocyclic quaternary ammonium cations in general have suitably high cathode discharge potentials for use in the present invention and readily form salts having suitably high water solubility with anions suitable for use in the electrolytes employed in the present invention. The saturated, aliphatic or heterocyclic quaternary ammonium salts aretherefore in general Well adaptedto dissolving high amounts. of olefinic carboxylates in their aqueous solutions and to effecting reductive couplings of such olefinic compounds. It is understood, of course, that it is undesirable that the ammonium groups contain any reactive groups which might interfere to some extent with the reductive coupling reaction. In this connection it should be noted that aromatic unsaturation as such does not interefere as benzyl substituted ammonium cations can be employed; (as also can aryl sulfonate anions).

Among the anions useful in the electrolytes, the aryl and alkaryl sulfonic acids-are especially suitable, for ex ample, salts of the following acids: 1 benzenesulfonic acid, 0-, mor p-toluenesulfonic acid, 0-, mor p-ethylbenzenesulfonic acid, 0-, mor p-cumenesulfonic acid, 0-, mor p-tert-amylbenzenesulfonic acid, 0-, mor p-hexylbenzenesulfonic acid, o-xylene-4-sulfonic acid, 'P-XYIeHC Z-SHL tonic acid, m-Xylene-4 or 5 sulfonic acid, inesityleneZ-sulfonic acid, durene-3-sulfonic acid, pentamethylbenzenesulfonic acid, o-dipropylbenzene-4-sulfonic acid, 'alphaor beta-naphthalenesulfonic acid, 0-, rnor p-biphenylsulfonic acid, and alpha-methy-l-beta-naphthalenesulfonic acid. Alkali metal salts are useful in the present invention with certain limitations, and thealkali metal salts of such sulfonic acids can be cmployed, i.e., the sodium, potassium,

lithium, cesium or rubidium salts such as sodium benzenesulfona-te, potassium p-toluenesulfonate, lithium o-biphenylsulfonate, rubidium bet-a-naphthalenesulfonate, cesium p-ethylbenzenesulfonate, sodium o-xylene-3-sulfonate, or potassium pentamethylbenzenesulfonate. The salts of such sulfonic acids may also be the saturated, aliphatic amine or heterocyclic amine salts, e.g., the mono-, dior trialkylamine salts, or the mono-, dior trialkanolamine salts, or the piperidine, pyrrolidine, or morpholinc salts, e.g., the ethylamine, dimethyl-amine or triisopropy-iamine salt of benzenesulfonic acid or of o-, por m-toluenesulfonic acid; the isopropanolamine, dibutanolamine or triethanolamine salt of o-, por m-toluenesu-lfonic acid or of o-, por m-biphenylsulfonic acid, the piperidine salt of alphaor beta-naphthalenesu'lfonic acid or of the cumenesulfonic acids; the pyrrolidine salt of mor p-amylben- Zenesulfonate; the morpholine salt of benzenesulfonic acid, of o-, mor p-tolucnesulfonic acid, or of alphaor betanaphthalenesulfonic acid, etc. In general, the sulfon-ates of any of the ammonium cations disclosed generically or specifically herein can be employed in the present invention. The aliphatic sulfonates are prepared by reaction of the correspondingly substituted ammonium hydroxide with the sulfonic acid or with an acyl halide thereof. For example, by reaction of a sulfonic acid such as p-toluenesulfonic acid with a tetraalkylammonium hydroxide such as tetraethylammonium hydroxidethere is obtained tetraethylammonium p-toluenesulfonate, use of which in the presently provided process has been found to give very good results. Other presently useful quaternary ammonium sulfonates are e.g., tetr-aethylammonium 0 or mtoluenesulfonate or benzenesulfonate; tetraethylammonium o-, mor p-cumenesulfonate, or o-, mor p-ethylbenzenesulfonate, tetramethylammonium benzenesulfonate, or o-, mor ptoluenesulfonate; N,N-di-rnethyl piperidinium o-, mor p-toluenesulfonate or -o-, mor pbiphenylsulfonate; tetrabutylammonium alphaor betanaphthalenesulfonate or o-, mor p-toluenesulfonate; tetrapropylammonium o-, mor p-amylbenzenesulfonate or alpha-ethyl-beta-naphthalene sulfonate; tetraethanolammonium o-, mor p-cumenesulfonate or o-, mor p-toluenesulfonate; tetrabutanolammonium benzenesulfonate or p-xylene-3-sulfonate; tetrapentylammonium o-, mor ptoluenesulfonate or o-, mor p-hexylbenzenesulfonate,

tetrapentanolammonium p-cymene-3-sulfonate or benzenesulfonate; methyltriethylammonium o-, mor p-toluene.

sulfonate or mesitylene-Z-sulfonate; trimethy-lethylammonium o-xylene-4-sulfonate or o-, mor p-toluenesulfonate; triethylpentylammonium 'alphaor beta-naphthalenesulfonate or o-, mor p-butylbenzenesulfonate, trimethylethanolammonium benzenesulfonate or o-, mor p-toluenesulfonate; N,l I-di-ethylpiperidinium or N-methyl-pyrrolidinium, o-, mor p-hexylbenzenesulfonatc or o-, mor ptoluenesulfonate, N,N-di-isopropyl or N,N-di-butylmorpholinium o-, mor p-toluenesulfonate or o-, mor pbiphenylsulfonate, etc.

The tetraalkylammonium salts of the aryl or alkarylsulfonic acids are generally preferred for use as the salt constituents of the electrolysis solution because the electrolyses in the tetraalkylarnmonium sulfonates are exclusively electrochemical processes. Employing the same concentration of alpha,beta-olefinic compound, the same cathodic voltage, but using the alkali metal sulfonates instead of the tetraalkylammonium sulfonates, yields of hydrodimerization products are markedly lower than those obtained with the tetraalkylammonium sulfonates. This is true even when there is present in the catholyte the high concentration of olefinic compound which can be attained by employing with the alkali metal sulfonate a co-solvent such as dimethylformamide. This is probably because at cathode voltages at which the hydrodimerization takes place, the alkali metal salts are also affected. Particularly when solutions containing the alkali metal sulfonates are stirred, the cathodic voltage necessary for hydrodimerization results also in discharging some alkali metal ions. Owing to the presence of these resulting metals, a chemical path is taken which results also in formation of the saturated monomer, rather than the hydrodimerization product. In the case of ethyl acrylate, for example, ethyl propionate is also obtained as by-product. This probably occurs by 1,4- or 1,2- addition of the alkali metal ion to the acrylate and decomposition by water of the resulting addition product to give the propionate. Whereas, according to the presently provided process, the two competing reactions, i.e., the formation of hydrodimerization products versus formation of saturated monomer, can be manipulated to favor the hydrodiinerization, nevertheless, some saturated monomer is formed when the electrolysis solution contains the alkali metal sulfonates rather than the tetraalkylammonium sulfonates, and the yield of hydrodimer is thereby decreased. On the other hand, purely chemicalreaction does not take place when the tetraalkylammonium sulfonates are used instead of the alkali metal sulfonates. This is because at cathodic voltages which favor the hydrodimerization reaction, the tetraalkylammonium ion is not discharged. In the case of ethyl acrylate for example, the optimum cathode voltage for conversion to the hydrodiinerization product (diethyl adipate) is of the order of about 1.85, as determined in a stirred run (versus the saturated calomel electrode). There is no lowering in yield of hydrodimerization product by chemical mediation such as, that which occurs by use of the alkali metal sulfonates, for the tctraalkylamrnonium ion is not discharged at the operating voltage. For example, tetraethylammoniumion is not discharged until about 2.5 cathodic volts. On the other hand, some olefinic compounds are hydrodimerized. at less negative cathodic voltages, permitting suitable resalts to be obtained with salts of alkali metals. However,

in order to insure against interfering reactions it is advantageous to employ salts of cations which have more strongly negative discharge potentials, e.g., more negative than 2.2 cathodic volts vs. the saturated calomel electrode.

Among the ammonium and amine sulfonates useful as electrolytes in the present invention are the alkyl, aralkyl, and heterocyclic amine and ammonium sulfonates, in which ordinarily the individual substituents on the nitrogen atom contain no more than 10 atoms, and usually the amine or ammonium radical contains from 3 to 20 carbon atoms. It will be understood, of course, that diand polyamines and diand poly-ammonium radicals are operable and included by the terms amine and ammonium. The sulfonate radical can be from aryl, alkyl, alkaryl or aralkyl sulfonic acids of various molecular weights up to for example 20 carbon atoms, preferably about 6 to 20 carbon atoms, and can include one, two or more sulfonate groups. Any of the quaternary ammonium sulfonates disclosed and claimed in my copending application S.N. 75,123 filed December 12, 1960, and now abandoned, can suitably be employed.

Another especially suitable class of salts for use in the present invention are the alkylsulfate salts such as methosulfate salts, particularly the amine and quaternary ammonium methosulfate salts. Methosulfate salts such as the methyltriethylammonium, tri n-propylmethylammoniurn, triamymethylammonium, tri n butylrnethylammonium, etc., are very hygroscopic, and the tri-n-butylmethylammonium in particular forms very concentrated aqueous so lutions which dissolve large amounts of organic materials. In general the amine and ammonium cations suitable for use in the alkyl-sulfate salts are the same as those for the sulfonates.

Various other cations are suitable for use in the present invention, e.g., tetraalkylphosphonium and trialkylsufonium cations, particularly as sulfonate salts formed from sulfonic acids as described above, or as methosulfatesalts.

' As a further illustration of electrolytes suitable for use in the present invention, the following named salts have all successfully been employed in hydrodimerizations to obtain hydrodimers as the major product with little or no formation of impurities, generally employing concentrated 11 aqueous solutions of the salts containing at least 15% and usually 20 to 40% by weight olefin, and utilizing the gen eral procedures of the illustrative examples herein:

(1) N-trimethyl-N'-trimethylethylenediammonium (ii -p toluenesulfonate (2) Benzyltrimethylammonium p'toluenesulfonate (3) Methyltri-n-butylphosphonium p-toluenesulfonate (4) Tetraethylammonium sulfate (5) Di-tetraethylammonium benzenephosphonate (6) Trimethylsulfonium p-toluenesulfonate 7) Methyltri-n-hexylammonium p-toluenesulfonate (8) Benzyltrimethylammonium phosphate (9) Benzyltrimethylammonium acetate (10) Methyltri-n-butylammonium methosulfate (ll) Benzyltrimethylammonium benzoate (l2) Tetraethylammonium methanesulfonate (1 3) Benzyltrimethylammonium 2-naphthalenesulfonate (l4) Bis benzyltrimethylammonium m benzenedisulfonate (l5) Benzyltrimethylammonium thiocyanate (16) Tetramethylammonium methosulfate Various other quaternary ammonium, tetraalkylphosphonium or trialkylsulfonium salts can be employed, in the process in general as well as in the hydrodimerization of ethyl acrylate in particular, e.g., the halides, sulfates, phosphates, phosphonates, acetates. and other carboxylic acid salts, benzoates, phosphonates, etc., specifically, for example, tetramethylammonium bromide, tetraethylammonium bromide, tetramethylammonium chloride, tetraalkylphosphonium chloride, tetraethylammonium phosphate, etc., and similarly thealkali, alkaline earth and other metal salts with the foregoing anions can be employed, e.g., sodium chloride, potassium phosphate, sodium acetate, calcium acetate, lithium benzoate, calcium chloride, rubidium bromide, magnesium chloride, as well as the sulfonic acid, particularly aromatic sulfonic acid, and alkylsulfuric acid salts of the foregoing cations and of other alkali, alkaline earth, rare earth and other metals, e.g., cesium, cerium, lanthanum, yttrium, particularly with anions to achieve suflicient water solubility. The aluminum cation is only somewhat inferior to sodium in respect to its discharge potential, but most salts of aluminum tend to hydrolyze in water and pre cipitate aluminum oxide. It is understood that the solutions designated herein as containing salts, electrolytes, etc.; in specified amounts have reference to solutions containing salts sufliciently stable to remain in solution. It will be recognized that many cations are capable of existing in several valence states, and some valence states will be more suitable as supporting electrolytes than others. Other examples of salts which can be employed in thelpresent process, although not necessarily with equivalent or optimum results, are barium bromide, barium acetate, barium propionate, barium adipate, cerium sulfate, cesium chloride, cesium benzoate, cesium benzenesulfonate, potassium oxalate, potassium sulfate, potassium ethyl sulfate, lanthanum acetate,

lanthanum benzene sulfonate, sodium sulfate, sodium potassium sulfate, strontium acetate, rubidium sulfate, rubidium benzoate, trisodium phosphate, sodium hydrogen phosphate and sodium bicarbonate.

Solubility will to some extent set an upper limit on salt concentration in the electrolyte solution, although if considered on the basis of Water solubility in the salt, fairly low concentrations of water can be employed, but in general there will be at least 5% or so by weight of water or other proton donor present to avoid excessive production of higher polymeric materials, and water will generally constitute more than or 20% by weight of the catholyte.

-In conducting the electrolysis process batch-wise and on a laboratory scale, the following procedure and apparatus may be employed; The electrolytic cell will comprise a container of material capable of resisting the 12 action of the electrolytes, e.g., glass. Within the container, and serving to divide it into an anode compartment and a cathode compartment may-be a diaphragm in the form of a porous cup, e.g., of unglazed porcelain. The anode, which can be of, e.g., platinum or carbon, or any electrode which is inert under the reaction conditions, is immersed in an anolyte contained in the porous cup. The anolyte is an aqueous solution of the salt. When there is employed no diaphragm in the cell, stirring can be employed for pH control. Thereby the anode is subjected to little or no attack; so that the anode can be of substantially any electrode material. An anode comprising lead deposited. on a copper screen can thus be employed. The cathode, which may be mercury, lead or another metal, and the porous cup, if one is employed, are submerged in the solution of alpha,betamono-olefinic carboxylate in the concentrated aqueous salt or a mixture of the same with a polar solvent. The entire cell may be cooled by a jacket containing a coolant, and both the anode a'nd'cathodechambers may be equipped with condensers. However, as will be hereinafter shown, the increase of temperature which is produced during electrolysis generally does not result in so much of a decrease in yield that cooling other than with circulating water is economically required. Generally, the electrolysis can, for example, be conducted at a tem perature of from, say, less than about 10 C. and up to almost the refluxing temperature of the electrolytic bath and at higher temperatures under pressure. Actually, slightly higher than ordinary ambient temperatures are conducive to improved yields, higher nitrile 'solubilities and lowered electrical resistance. This is to some extent counterbalanced by the tendency of some'diaphragm to C. Stirring of the solution during the electraction, fractionation, etc.

trolyses, if desired, maybe conducted by mechanical or magnetic means. During the electrolysis, thepH of the catholyte may be controlled as hereinbefore described.

The quantity of current which is supplied to the cell will vary with the nature and quantity of the bath and of the electrodes and with the operating temperature, but will ordinarily be at a rate greater than 0.5 ampere and in the order of a current density of, say, from 2.0 to 20.0

or 40 or more amperes/dm. (dm? refers to the area in square decimeters of cathode surface). The efficiency of the process is, to some extent, dependent on the current density used. Thus for the efiicient production of dialkyl adipates the current density should be at least about 5 amperes/dm. and practical production rates ordinarily require the use of much higher currentdensities.

Itis important to note th-atthe present process involves an actual electrochemical reduction in which an electric potential is actually applied to a solution of the olefinic carboxylate and current passed therethrough while the solution is in contact with the cathode, thereby involving a radical departure from such indirect methods as preparing sodium amalgam by electro-chemical reduction of sodium salts followed by mere contacting of a solution of an olefin with the sodium amalgam.

After the electrolysis, the hydrodimerization product may be separated from the reaction mixture by isolating procedures known to those skilled in the art, e.g., by ex- Generally, the reaction mixture is neutralized and,'after dilution, the organic phase is separated by decanting and/or solvent extraction. After removing any residual inorganic matter by washing with water, the organic material is distilled to remove solvent and to give as residue the hydrodimerization product and any unconverted olefinic carboxylate, together with by-products, if any. These may be separated from each other, e.g., by fractional distillation, etc. In experimental runs, results of the electrolysis can be conveniently arrived at, when the products are liquid, simply by analytical determination of the hydrodimerization product and of the unconsumed monomer, if any, e.g., by vapor phase chromatography.

The following equations are illustrative of the proposed mechanism of the process of the present invention which occurs under non-acidic conditions at suitable cathodic potentials and suitable concentrations:

CH CHCO Et C G CO2Et Ethyl acrylate H 2e C: C: COgEl:

1.9 volts Ca. 1.5 volts H H 1v+n+ 6.6mm

ii ii (V) V ethyl acrylate polyacrylate and to that which produces pinacols from ketones C=O l-I+ e R/ R It will be noted that the proposed mechanism to adipates avoids the free radical V, as would appear essential for any mechanism to have validity in view of the known propensity of acrylates to polymerize in the presence of free radicals. The proposed addition of two electrons to one molecule and its coupling with a molecule to which no electrons have been added is also supported by results described in my copending application S.N. 163,028 filed December 29, 1961, which relates to coupling of two diferent olefinic compounds at cathodic potentials sufficient to supply electrons to only one of the olefinic compounds. The proposed mechanism to adipates also explains the significance of the acrylate concentration. For if the ion II encounters a high concentration or" water molecules, rather than acrylate molecules, it will take up two hydrogen ions from the water to form a propionate; thus it is necessary to maintain a high acrylate concentration to avoid or minimize this simple reduction. Similarly, hydrogen ions present under acidic conditions enter into an interfering reaction with ion II by adding to II to form a propionate. While water molecules can interfere, some water or other source of proton donor is necessary to provide hydrogen to convert III to ethyl adipate and to avoid a tendency toward polymerization. Thus the catholyte will ordinarily comprise by weight or more water, although even a few percentage points of water is ordimixture allowed to stand for 30 minutes.

Id narily sufficient. Of course, a certain minimum of water is advantageous in lowering electrical resistance.

The applicant does not intend to be limited to any particular mechanism, as the demonstrated results are obtained regardless of the mechanism advanced in explanation thereof. The proposed mechanism will aid in unstanding the process and in explaining the significance of certain departures from the prior art and of certain requirements for the process.

It is desirable to avoid acidity in order to effect the process of the present invention, both because of interfering polymerization reactions which occur in acidic media, and because of the discharge of hydrogen ions which occurs circa -l.5 volts. If only a small amount of hydrogen ions are present at the start of electrolysis, it may be simple to electrolytically discharge such ions at the cathode until the pH goes over 7 and then to proceed with the hydrodimerization while maintaining alkaline conditions.

The invention is further illustrated by, but not limited to, the following examples:

Example 1 Tetraethylammonium p-toluenesulfonate was prepared as follows: A' mixture consisting of 200 g. (1 mole) of ethyl p-toluenesulfonate, 101 g. (1 mole) of triethylarnine and ml. of absolute alcohol was stir-red at room temperature for 3.5 hours and then heated to 72 C., within 40 minutes. At this point an exothermic reaction occurred, and extraneous heating was discontinued and the At the end of that time it was heated to reflux, and refluxing was continued for 6 hours. After being allowed to cool to room temperature, the solvents and any unreacted material was stripped off with an aspirator to obtain a residue which solidified. This was washed with absolute ether three times by decanation. After removing traces of solvent from the washed product with an aspirator, there was obtained as residue 296.8 g. of the substantially pure tetraethylammonium p-toluenesulfonate, M.P. 103-104 C. An electric current was passed through a cell containing as catholyte a solution consisting of 91.0 g. of ethyl acrylate containing a trace of p-nitrosodimethylaniline as stabilizer, 90 g. of 75% by weight aqueous tetraethylammonium p-toluenesulfonate solution and 68 g. of dimethylformamide, and an anolyte consisting of 20 ml. of water and 20 ml. of said 75 sulfonate solution. The cell was composed of a platinum anode placed in an Alundum cup containing the anolyte and immersed in a jacketed glass vessel containing the catholyte and ml. of mercury as cathode. During the 3-hour electrolysis period which was employed the cell voltage was from 37.5 to 26.5 volts during the first hour and then from 26.5 to 22.0 volts during the last two hours; and the operation was conducted for 7.3 amp-hrs. The pH of the catholyte was neutral before the electrolysis and during the electrolysis as alkalinity was built up it was maintained just alkaline to phenol red by intermittent addition of -a total of 3.20 ml. of glacial acetic acid. Also, in order to maintain the clarity of the catholyte, small additional amounts of dimethylformamide were added to the catholyte on three occasions. During the electrolysis, the temperature of the catholyte was allowed to increase from 22 C., to 35 C. The cathode voltage measured against a saturated calomel electrode for the hydrodimerization of ethyl acrylate is 1.85.

At the end of the electrolysis, the catholyte was extracted 6 times with methylene chloride, back-washed twice with water, dried over potassium carbonate and subsequently concentrated to remove the methylene chloride and further stripped of volatiles by an aspirator to give 28.1 g. of residue. Vacuum distillation of the residue gave as the bulk-of the product the substantially pure diethyl adipate, B.P. 142-150 C./3O mm., 11 1.4255. A sample thereof, submitted for spectrophotometric anal- 15 ysis showed the known, characteristic spectrum of diethyl adipate. The yield of diethyl adipate was 74-75%, based on ethyl acrylate reacted.

- Example 2 This example describes the electrolytic hydrodimerization of diethyl maleate. Q

Employing the apparatus, electrodes and anolyte described in Example 1, an electric current was passed for 4 hours through a cell containing as catholyte a mixture consisting of 105 g. of diethyl maleate, 106 g. of 75% by weightyaqueous tetraethylammonium p-toluene'sulfonate, and 47.6 g. of dimethylformamide. During the electrolysis, the temperature of thecatholyte was kept at 2230 C., by means of jacket-cooling, there was em ployed a cell voltage of 33-369 volts, and the cathode voltage against the saturated calomel'electrode was found to rise from 1.25 to 1.40 volts. There was employed a current of from 0.5 to 2.0 amps. during the first 2 hours and from 2.0 to 2.9 during the remaining 2 hours, or a total of about 8.1 amp.-hrs. The pH of the catholyte was maintained just alkaline to phenol red by intermittent addition of a total of 2.55 ml. of glacial acetic acid and development of turbidity in the catholyte was obviated by periodic addition of very small quantities of dimethylformamide.

'; After passage of current was was transferred from the cell, extracted 4 times with 50 ml. portions of methylene'chloride, back-washed twice with water and dried over a drying 'aid and filtered. The methylene chloride was stripped from the filtrate by distillation to give 124.2 g. of residue, a 10% aliquot of which was submitted for vapor phase chromatographic analysis. The remainder was fractionated through a Vigreux column to give a fraction, B.P. 103 C. 12 mm. (or 104 C./ 14 mm.) which was unchanged starting material. The residual liquid was distilled without a column to give the bulk of the product, the substantially pure tetraethyl butane 1,2,3,4 tetr-acarboxylate, B.P. 168- 172 C./0.65 mm analyzing 55.52% carbon and 7.86% hydrogen as against 55.48% and 7.57%, the calculated values. r

Example 3 7 period the temperature of the catholyte was maintained at from 22-27 C. and the pH of the catholyte was maintained just alkaline to phenol red by the intermittent addition of a total of 4.20 -ml. of acetic acid. Operation was conducted at a cell voltage of 27.3 to"36.5 volts and a cathode voltage as determined against the saturated calomel electrode of -1.90 to 2.18 forv about 6.0

amp-hrs. a Whenthe current was discontinued, the catholyte was neutralized withacetic acid and extracted with four ml. portions of methylene dichloride. After washing the combined extracts with water and drying, the methylene dichloride was stripped off to obtain as residue 145.2 g. of material which upon fractional distillation gave the substantially pure diethyl 3,3,4,4-tetramethyladipate, B.P. 128/1.7 mm, 11 1.4480, in a yield of 66.2% based on the electric current employed.

Cryoscopic molecular weight determination in benzene and in biphenyl gave a molecularweightof 258 as against 258.35, the calculated value.

discontinued the catholyte Example 4 Diethyl ethylidenemalonate was hydrodimerized utilizing a catholyte containing 95 grams of the esterin 95 grams of an 80% solution of tetraethylammonium p-toluenesulfonatein water together with 62 grams of dimethylformamide. The cathode was 110 ml. Hg and a total of 1.7 ml. acetic acid was intermittently added to avoid excessive alkalinity. The electrolysis was conducted with a current of about 2.5 amperes for about 1.5 hours with cathodic voltages of 1.59 to 1.68. The product was extracted with methylene dichloride, and after washingwith waterjdrying over Drierite, and evaporation of the methylene dichloride, the product was distilled at 147157 C./0.35-0.45 mm. in an amount of 50.9 grams. The desired hydrodimer, tetraethyl 2,3- dimethylbutane l,1,4,4 tetracarboxylate, obtained in a yield of 78% based on 'monomer reacted, analyzed as followsCalcd: C, 57.71; H, 8.08. Found: C, 57.65; H, 8.06.

When the procedure of the foregoing examples is followed, but employing only'about 10% ,by weight tetraethylammonium p-toluenesulfonate and as much of the olefinic carboxylate, for example that of Example 1, as will dissolve fairly substantial yields of the corresponding'hydrodimer are obtained, although markedly inferior 'to' those obtained at higher carboxylate concentrations.

However when the tetraethylammonium p-toluenesulfonate concentration is 1%, the yields utilizing comparable olefinic carboxylate concentrations are much lower and of little practical significance. For this reason the concentration of the saltcatholyte is important to the results attained.

Example 5 Following the general procedure of Example 1 but employing a 5% byweight solution of NaCl as catholyte and slightly over 5% by weight ethyl acrylate, a very small amount of diethyl adipate can be obtained.

Example 6 7 By substituting strontium chloride for the sodium chloride in Example 5, a similarly small amount of diethyl adipate can be obtained.

The aboveexamples and data are illustrative'of the hydrodimerization of alpha,beta-mono-olefinic carboxylates. Specific process conditions may vary, of course, with different cell structures, with ratio of volume of catholyte to surface area of cathode as Well as with other variables such as temperature, cathode voltage, current density, etc. Moreover, a number of cells can be combined into a single unit, and the process can be carried out continuously by means of a circulating pump whereby the catholyte is withdrawn from the cell during the process, the hydrodimerization product is separated therefrom, and the residue is reintroduced into the cell togther with additional olefinic compound to make up the initial strength.

The presently provided process provides a very simple and economical method for the manufacture of a great .'many aliphatic poly-functional compounds, particularly the diand tetra-esters. The electrolytic process of this invention is advantageous in that, during the electrolysis,

"electrolyte is not consumed, only a minor proportion, if

any, of the olefinic monomer is converted to the saturated monomer and the'electrolysis can be conducted if desired withoutthe use of cost-increasing cooling systems and with highly eflicient utilization of electric current.

;The process of this invention is particularly useful in those instances in which the dior tetra-functionalalkanes have beenfobtainable only with difiiculty or. not at all by other processes. By hydrodimerizing a mono-olefinic carboxylate it often is possible to obtain, using the process of this invention, av branched paraflinic carboxylate more easily and more economically than otherwise would be possible. The parafiinic dicarboxylates prepared by the present process are generally useful in the manufacture 17 of high-molecular weight condensation polymers, e.g., by reaction with dihydroxy or'dicarboxylic compounds; and the tetra-functional compounds, as well as the difunctional compounds, are eificient plasticizers for synthetic resins and plastics.

It is obvious that many variations may be made in the process of this invention without departing from the spirit and scope thereof.

What is claimed is:

1. A method of producing hydrodimers of aliphatic alpha,beta-mono-olefinic carboxylates in substantial yield which comprises subjecting a solution of an olefinic compound selected from the group consisting of the alkyl and aryl esters of aliphatic alpha,beta-mono-olefinic acids to electrolysis by passing an electric current through said solution in contact with a cathode, causing development of the cathode potential required for hydrodimerization of the olefin compound, the solution consisting essentially of water, more than about by'weight of the olefin compound, and at least 5% by weight of supporting electrolyte salt to make the solution conductive, and recovering in substantial yield hydrodimer in which coupling has occurred between corresponding carbon atoms of two molecules of the starting ester, the said carbon atoms being in the beta-position of the olefinic bond with respect to an ester group of the starting ester, the said hydrodimer having twice the carbon atoms of the starting ester, the said electrolysis being conducted in a cell in which both cathode and anode are in actual physical contact with electrolyte.

2. A method of producing hydrodimers of aliphatic alph-a,beta-mono-olefinic carboxylates in substantial yield which comprises subjecting a solution of an olefinic compound selected from the group consisting of the alkyl and aryl esters of aliphatic alpha,beta-mono-olefinic acids to electrolysis by passing an electric current through said solution in a divided cell in contact with a cathode under substantially non-polymerizing conditions, causing development of the cathode potential required for hydrodimerization of the ester, the solution comprising water, more than about 5% by weight'of the ester and to make the solution conductive at least 5% by weight of a supporting electrolyte salt which provides a cation discharging at cathode potentials more negative than that at which hydrodimerization of the ester occurs and more negative than that at which sodium discharges, and recovering in substantial yield hydrodimer having twice the carbon atoms of the starting ester, the said electrolysis being conducted in a cell in which both cathode and anode are in actual physical contact with electrolyte.

3. The method of claim 1 in which a divided cell is employed in which the average olefin compound concentration is greater than 15 by weight of the catholyte.

4. The method of claim l in which the pH in the bulk of the solution is in the range of about 6 to about 12.

5. The method of claim 1 in which the salt provides a cation discharging at substantially more negative cathode potentials than that at which the hydrodimerization of the olefin compound occurs and the cathode employed has a hydrogen overvoltage greater than that of copper.

6. The method of claim 1 in which a divided cell is employed and the catholyte is prevented from becoming excessively alkaline by providing acid thereto to counteract the alkalinity developed by discharge of ions at the cathode.

7. The method of claim 2 in which the salt concentration constitutes more than 30% by weight of the salt and water present in said solution.

8. The method of claim 1 in which the cathode is lead.

9. The process of claim 1, further limited in that the olefinic compound is an alkyl ester of an alpha,beta-monoolefinic carboxylic acid having from 1 to 5 carbon atoms in each alkyl radical and from 3 to 8 carbon atoms in the acid portion of the molecule.

10. The process of claim 1, further limited in that the 18 olefin compound is a dialkyl ester of a methylene malonic acid.

11. The method of claim 1 in which the hydrodimerization is conducted at a cathode potential no less negative than l.7 volts.

12. The method of claim 1 in which a polymerization inhibitor is employed.

13. The method of claim it in which the aqueous electrolyte comprises a salt selected from the group consisting of amine and ammonium sulfonates and alkylsulfates.

14. The method of claim 1 in which the pH is maintained in the range of about 7 to about 9.5.

15. A process for conducting the hydrodimerization of an alkyl ester of an alpha,beta-mon-o-olefinic aliphatic acid of from 3 to 8 carbon atoms, which comprises subjecting to electrolysis, in contact with a cathode having a hydrogen overvoltage greater than that of copper, a solution comprising water, the ester, and a saturated tetraalkylarnmonium salt of an alkaryl sulfonic acid wherein the total number of carbon atoms in the sulfonic acid is from 7 to 12 and the total number of carbon atoms in the salt-forming radical is from 4 to 20, the concentration of the olefinic ester in the solution being from about 10% to 50% by Weight of the solution, the concentration of said salt in the solution being above about 30% by Weight of the total amount of water and salt present in said solution and up to saturation.

16. A process for conducting the hydrodimerization of an alkyl ester of an alpha,beta-mono-olefinic aliphatic carboxylic acid having from 1 to 5 carbon atoms in each alkyl radical and from 2 to 8 carbon atoms in the acid portion of the molecule, which comprises subjecting to electrolysis, in contact with a cathode having a hydrogen overvoltage greater than that of copper, a solution comprising water, the ester, and a salt selected from the class consisting of the saturated aliphatic and heterocyclic amine salts and the saturated aliphatic and heterocyclic quaternary ammonium salts of an alkyl sulfate wherein the alkyl sulfate ion has no more than 8 carbon atoms'and the total number of carbon atoms in each of said amine and ammonium salt-forming radicals is from 3 to 20, the concentration of the ester in the solution being from about 10% to 50% by weignt of the solution, the concentration of said salt in the solution being above about 30% by weight of the total amount of water and salt present in said solution and up to saturation, and the pH of the solution being above 7 but below the value at which substantial hydrolysis of the alkoxycarbonyl group of the ester occurs.

17. The process for conducting the hydrodimerization of diethyl maleate which comprises subjecting to electrolysis, in contact with a cathode having a hydrogen overvoltage greater than that of copper, a solution comprising water, diethyl maleate and tetraethylammonium p-toluenesulfonate, the concentration of the maleate in the solution being from about 10% to 50% by weight of the solution, the concentration of said sulfonate in the solution being above about 30% by weight of the total amount of water and sulfonate present in said solution and up to saturation, and the pH of the solution being above 7 but below the value at which substantial hydrolysis of the maleate occurs.

18. The method of claim 1 in which the olefin compound is ethyl acryl-ate.

19. The method of claim 2 in which the pH in the bulk of the solution is in the range of about 6 to 12.

20. The method of claim 1 in which a polar solvent is employed along with water.

21. A method of producing hydrodimers in better than 50% yield which comprises subjecting a solution of an olefinic compound selected from the group consisting of the alkyl and aryl esters of aliphatic alpha,beta-mono olefinic acids to electrolysis by passing an electric current through said solution in contact with a cathode having an overvoltage greater than that of copper under substantially non-polymerizing conditions, the current density 7 the solution comprising water, more than 10% by weight of the olefinic compound and supporting electrolyte salt to make the solution conductive, the amount of salt being above about 30% by weight of the total amount of salt and water present in said solution, the salt providing a cation discharging at cathode potentials more negative than that at which hydrodimerization of the olefinic compound occurs, and more negative than that at which sodium discharges, and obtaining in better than 50% yield hydrodimer having twice the carbon atoms of the starting olefinic compound. t

22. The method of claim 21 in which the pH in the bulk of the solution is above 7 but below about 9.5.

23. The method of claim 21 in which a divided cell is employed so that the solution of olefinic compound does not contact the anode.

24. The method or claim 21 in which a tetraalkylammonium alkyl sulfate salt is used as electrolyte.

25. The method of claim 21 in which a tetraalkylammonium aromatic sulfonate salt is used as electrolyte.

26. A process for conducting the hydrodimerization of an aliphatic olefinic compound which is an alkyl ester of an alpha,beta-mono-olefinic carboxylic acid having from 1 to 5 carbon atoms in each alkyl radical and from 3 to 8 carbon atoms in the acid portion of the molecule, which comprises subjecting to electrolysis, in contact with a cathode having a-hydrogen overvoltage greater than that of copper, a solution comprising water, the olefinic compound, and a salt selected from the class consisting of the saturated aliphatic and heterocyclic amine salts and the saturated aliphatic'and heterocyclic quaternary ammonium salts of a sulfonic acid selected from the class consisting of aryl and alkaryl sulfonic acids wherein the total number of carbon atoms inthe sulfonic acid is from 6 to 12 and the total number' of carbon atoms in each of said amine and ammonium salt-forming radicals is from 4 to 20, the concentration of the olefinic compound in the solution being from about 10% to 50% by weight of the solution, the concentration of said salt in the solution being above about 30% by weightof the total amount of water and salt present in said solution and up to saturation, the pH of the solution being above 7 but below the value at which substantial hydrolysis of the alkoxycarbonyl of the ester occurs, and the said electrolysis being conducted in a cell in whichboth cathode and anode are in actual physical contact with electrolyte.

FOREIGN PATENTS 566,274 11/58- Canada.

JOHN H. MACK, Primar Examiner. I HOWARD s. WILLIAMS, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,193,482 July 6, 1965 Manuel Mu Baizer It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 56, for "consisting" read constituting column 2, line 41, for "which" read when column 10, line 68, for "trialkylsufo-" read trialkylsulfocolumn 14, line 6, for "un" read under line 37, for "decanation" read decantation column 18, line 31, for

"2" read 3 Signed and sealed this 31st day of May 19660 (SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER A Lttesting Officer Commissioner of Patents 

1. A METHOD OF PRODUCING HYDROLIMERS OF ALIPHATIC ALPHA, BETA-MONO-OLEFINIC CARBOXYLATES IN SUBSTANTIAL YIELD WHICH COMPRISES SUBJECTING A SOLUTION OF AN OLEFINIC COMPOUND SELECTED FROM THE GROUP CONSISTING OF THE ALKYL AND ARYL ESTERS OF ALIPHATIC ALPHA, BETA-MONO-OLEFINIC ACIDS TO ELECTROLYSIS BY PASSING AN ELECTRIC CURRENT THROUGH SAID SOLUTION IN CONTACT WITH A CATHODE, CASUING DEVELOPMENT OF THE CATHODE POTENTIAL REQUIRED FOR HYDRODIMERIZATION OF THE OLEFIN COMPOUND, THE SOLUTION CONSISTING ESSENTIALLY OF WATER, MORE THAN ABOUT 5% BY WEIGHT OF THE OLEFIN COMPOUND, AND AT LEAST 5% BY WEIGHT OF SUPPORTING ELECTROLYTE SALT TO MAKE THE SOLUTION CONDUCTIVE, AND RECOVERING IN SUBSTANTIAL YIELD HYDRODIMER IN WHICH COUPLING HAS OCCURRED BETWEEN CORRESPONDING CARBON ATOMS OF TWO MOLECULES OF THE STARTING ESTER, THE SAID CARBON ATOMS BEING IN THE BETA-POSITION OF THE OLEFINIC BOND WITH RESPECT TO AN ESTER GROUP OF THE STARTING ESTER, THE SAID HYDRODIMER HAVING TWICE THE CARBON ATOMS OF THE STARTING ESTER, THE SAID ELECTROLYSIS BEING CONDUCTED IN A CELL IN WHICH BOTH CATHODE AND ANODE ARE IN ACTUAL PHYSICAL CONTACT WITH ELECTROLYTE. 